The invention relates to a shifting arrangement for two clutches for the shifting between a single-axle standard drive and a two-axle all-wheel drive for a motor vehicle having two drivable vehicle axles.
A known shifting arrangement of this type (DE-OS No. 32 03 707), for a drive that is a permanent all-wheel drive per se, uses a fast-shifting clutch for the front axle in order to improve the driving characteristics in special operating situations. The shifting from the all-wheel drive to the rear wheel drive may take place automatically as a function of the steering angle, or manually via a switch.
The objective of the invention is to carry out, in the case of a shifting arrangement of the initially mentioned type, the shifting into the shift step for standard drive as fast as possible but mainly as smoothly as possible and without any sudden torque increase at the rear axle.
In the case of the shifting arrangement according to the invention, smooth and fast shifts are made possible because of the use of frictionally engaged clutches and pressure-medium-operated control elements. For shifting into the shifting step for the standard drive, a shift valve can be controlled by the control unit in such a way that, the clutch torque of the clutch of the differential gear increases at least approximately only to the extent to which the clutch torque of the clutch for one vehicle axle decreases.
The shift valve has an intermediate position in which the valve connection that is connected with the second control element of a second clutch of one vehicle axle is connected with the valve connection that is part of the switching step for the standard drive. An electronic function converter is connected between the shifting valve and the control unit for controlling the shift valve to pass through the intermediate position when shifting slowly through the intermediate position when the shifting signal for the shifting step for standard drive occurs and to pass rapidly through the intermediate position when the shifting signal for the shifting signal for a balanced all-wheel drive occurs.
In a first embodiment the two clutches are disengaged by spring force and engaged by auxiliary forces through their control elements. The valve connection that is connected with the first control element of the first clutch is connected with the valve connection that is connected with the second control element of the second clutch in the intermediate position.
In a second embodiment the first clutch is engaged by auxiliary force at its first control element and the second clutch is engaged by spring force. The valve connection of the shift valve that is connected with the first control element of the first clutch is continuously connected with the second control element of the second clutch and, in the intermediate position is connected with the valve connection for the storage tank. The intermediate position of the proportional valve in the second embodiment includes a throttle connection between the valve connection that is connected with the control elements and the pressure source.
In a third embodiment, the first clutch is engaged by spring force and the second clutch is engaged by the auxiliary force at the second element. The valve connection of the shift valve that is connected with the first control element of the first clutch is contacted continuously with the control element of the second clutch and in the intermediate position is connected with the valve connection of the shift valve for the pressure source. In the third embodiment the intermediate position includes a throttle connection between the valve connection connected with the control elements of the clutches and the valve connection for the storage tank.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.